Need opinions on mild 489 build
 

Hello,

I am putting together a relatively mild, budget minded (I know, budget boat engine is an oxymoron) 489 to run in a late 80's 25-ish Baja. I'll lay out my proposed buildup, ask a couple of specific questions, and then "hang up" and wait for your answers. :D

I am basing this on a .030 over Gen VI block, 4.280 x 4.25 stroke, flat top, shooting for around 9:1 with 119 cc chambers. I am planning to run a set of GM oval port 781 casting heads with some modest bowl blending and 2.19 1.7 valves (I'll cover the valve sizes in my follow up question). Cam specs I am planning to run will be around 225*/235* @ .050, .530 / .550, 114* LSA. I say "planning" because I am planning to have a stock GM billet Mag cam reground for a little more lift. If possible, I want to retain the stock GM roller lifters with the cam (already have a set - my stinginess is coming in here again).

Induction will be a reworked Q-Jet with 502 spec jetting on a Performer RPM, stock Merc exhaust manifolds with silent choice, and stock Thunderbolt IV ignition.

Like I said, the idea here is to build something with a budget in mind that will be durable and dependable, but give me tons of torque to swing a bigger prop for excellent cruising speed.

Questions:

#1) Am I on target for my cam selection? I realize some power is being left on the table with the lift, but once again, I am on a budget and am trying to avoid spending an extra $500 on a set of Morel lifters if I don't need to. Long term reliability also becomes a concern when you start to approach .600 valve lift and higher spring pressures. I went with the split duration just based on what I have seen for most other marine profiles - open to suggestions here.

#2) I promised to address my valve size choices earlier, so here goes. I already have a set of heads with the Ferea super-alloy exhaust valves in the 1.72 size. I figured this would be a good valve to retain for durability. Wish they were 1.88's, but it is what it is. My question: will having the 2.19's and 1.72's result in a poor intake/exhaust flow ratio? Or am I actually better off this way in light of the stock exhaust and relatively poor flow characteristics? I'm sure the bigger intake valves will help it inhale, but I am concerned that exhaust flow will not be good enough to take advantage of the better intake flow. Can this be addressed with the cam profile? Better flowing aftermarket exhaust is not in the budget, and I would like to maintain the switchable exhaust.

#3) Would hypereutectic pistons and steel cast crank survive OK in a boat that spends most of its life cruising, with an occasional WOT blast for a couple of minutes?

Looking forward to thoughts from everyone.

Thanks!

Unless you change the stock exhaust you will be wasting your time and money.
I have built several stroker engines and they are torque monsters.

I have used Cast Steel and did not have any problems. That being said I would never do it again.

You are not going to be a happy boater if you put an engine together and something breaks and you are sitting on the dock all summer.

If you decide to build an engine Get a hold of RMBUILDER (Bob Madra) for your cam selection.

I took a pair of brand new engines apart last year and changed the cams with the help of Bob. I also wanted to use the stock lifters since they where brand new. The max lift you can do is .550. You will need to change the springs to match the cam. I regret it to this day of not spending the extra money on new lifters. It limited my cam selection.

I thought the boat would have to much power with twin 502's but you can never go fast enough:drink:

I have two brand new Gen VI roller cams and springs, and retainers if you are interested..

Your Comp will with that setup will Not be 9 to 1, more like 8.6 to 1 or less. You will need either different heads with smaller chambers or small dome pistons.
You will NOT want to use the stock exhaust.
If your engine was originally a 330 HP engine you will have to upgrade the oiling system.
If you really want it to run call Bob RMbuilder, spend the money on better parts. And call him before you purchace any parts. I have been through all this before and wound up just wasting money.

Oh, and welcome to the site, I see its your first post.

What do you think if he was to use the factory 496 aluminum manifolds with the 9" tall, round stainless risers?

Of course, this question is a "496 Merc aluminum manifold verses the Merc cast ones"

I'm suggesting this idea, as you can pick up a pair of those 496 manifolds pretty reasonably...

Would there be any real difference between the two?

Look in the swap shop, there are 2 sets of EMI Thunders with long risers. These are the same ones I use, but these have the polished manifolds.

Thanks for the replies, guys. Not actually my first post - I used to post on here as Budman, but that was tied to an old email address that I no longer had, I forgot the password to that account, and the board gods couldn't fix it, so here I am with a new username counter and counter.

Yes, I am aware that the optimum solution would be forged crank and pistons, but there goes another grand. That is one of the reasons I was going to stay conservative on the compression ratio. I might reconsider on the pistons and go forged, but there are a lot of cast crank motors making 500 HP and above, and surviving OK. I had a cast crank in the last motor, and it was not the point of failure.

Jeffwav, are you saying that the stock Merc oil cooler will not be sufficient for a 489?

We are talking about a 30 year old boat that is worth maybe $10K in today's economy. Planning to keep it for a few more years, then move into something bigger/newer. Can't see me getting my money back out of it when I sell it as it is, so my hesitation in dropping more money into it is understandable.

Maybe I should drop back and punt and just drop in a stock motor. :confused:

Does the "Gen VII" 496 share the same exhaust flange pattern as the Mk IV/Gen V/VII engines?

Yep, saw those. There is also a guy on Speedwake selling a set of Lightnings that I thought about. Trouble with that is I would have to ditch the Silent Choice. I like to be loud like anyone else, but there are times when I want it quiet too. I would have to fork over another grand for a set of switchable tips then.

B.O.A.T. - Break Out Another Thousand.

OK, I know the advantages of aftermarket exhaust are the ability to run more overlap on the cam, better flow, elimination of Merc flange interface, etc. But I have also seen a lot of guys switch from the stock Merc stuff to the aftermarket manifolds and pick up some midrange torque and maybe 2 0r 3 MPH on the big end. Hard for me to justify shelling out another $1500+ based on that.

Thanks for the replies! And I'm not intentionally trying to shoot down suggestions - just trying to balance out limited funds. I have a couple of other toys to spend money on, and a wife and kids who are good at spending it for me too!

Go forged on the pistons. Too many people around here have broken cast ones. And it usually wipes out the whole engine. Srp makes a small dome forging that is a good buy. It will give you about 9.6 to 1 compression. I would also advise using longer rods in a build like this. 6.385 is the usual size for a .25 stroker. You should be ok using the stock exhaust. Years ago, I replaced a pair of 330's with a pair of 420's in a 30 Scarab. I used the stock log manifolds for a while and still gained 8 mph.

If you do not have the budget to do it correctly, maybe just build it to stock spec. Learn from my mistakes, if you try to cut corners you will just be redoing everything over and over again. Sounds like you are trying to cut way more corners than I did. The exhaust prevents reversion, that is created with bigger cams. How big is your oil cooler? If it is the size of a beer can then it is to small. Also the stock oil lines a fittings are only good for a stock engine, anything more and that will cause you problems.
I have spun berrings, broke a crank, had a cam go flat, blew a hole in a piston. Now that I have better exhaust, better oiling system, roller cam and all forged internals the engine is running strong and reliable. It just cost more money to make it work correctlly. Good luck with your project.

God I hope so! I have twin Gen V's and I'm stuck in the same "boat" you are...

I love the boat I'm re-working but, there is a limit to how much $$$$ to pour into it verses selling and moving up the ladder.

So far, I'm into my boat close to $8K, with another estimated $7 to $10K to go to get it finished how I want it...

When I bought the 496 (Aluminum) manifolds for my set-up, I was told that they would be a bolt-on to my 454 Mag heads (The rectagular port heads).

I'm not sure about any other application. I was also told that while these manifolds aren't considered to be a "performance" manifold, they would be tons better than the cast set-up I did have.

The small exhaust valves aren't your friends. You don't NEED the SuperAlloys (great material, but overkill for you), so figure out if you have a buyer for those nice (but small) valves and install 1.90's in a good stainless - or sell/swap the heads for some heads with bigger valves.

A regrind isn't a bad idea with roller lifters, but there are lots of decent available profiles and some low hour sticks available. Lightly used roller cams are an option.

Don't forget to bore-notch your cylinders. Your smallbore block partially shrouds the valves (especially if you are running the right sized ones). There are 25 horses hiding in that one spot.

Best of luck

Thanks for the reply, MCCOLLINS. Would the Ferrea 5000 series or 6000 series exhaust valves do the trick? Would you stick with the oval port 781's with the bigger valves, or go rectangle port? I can pick up a set of used rect port heads that already have the big valves for around $300. Would that kill the low-mid range power too much?

I have not heard of a 1.9 BBC exhaust valve. Would 1.88 work as well?

All of the 781 heads i find are the stock small valves..

Bore notch you mean cylinder heads??

IM doing a similar build now, bore out cylinders, new pistons probly cast, rm cam, sm exhaust, edlebrock intake,
found a set of 781 one heads but they have stock valves, im going to upgrade springs and valve components..

I wanted to find the bigger valves but cant ppl say it wont be much diff, and bigger valves barely fit in that small 110 cc head

Pantera, you are correct - 781 ovals (like all GM ovals) came with 2.09 / 1.72 valves. I was referring to whether it would be best to run a set of 781's with the larger valves installed, or just buy a set of square port heads that already have the 2.19 / 1.88.

Bore notching revers to putting a deep bevel at the top of the bores where the intake and exhaust open into the cylinder. Many of the factory high performance 4-bolt blocks had this. It unshrouds the valves when they open into the cylinder and promotes flow.

BTW, those 781 heads should have a 119 cc chamber, not 110 cc. Same chamber as the 088 and 990 square port heads commonly found on marine engines.

$300 is a good price for those heads. I would probably buy them to put on the shelf. If the valve's are good in them you could use them to switch over to the ovals if you wanted to stay with the ovals. Remember buy going to larger valves in the ovals you are also going to need some grinding work done to blend to the larger valve size. Also some unshrouding of the valves in the chambers. If it were a 454 I would deffinately say ovals. With the extra cubes you might be alright with the rectangular ports if you plan to spin it high. Hard decision as to which would actually be best but I'm think'n the ovals. Just re read your opening post and remember now you want a dependable budget build so I think I would deffinately go oval. Prop to keep under 5400rpm's. Here's an interesting link to a flow comparision between ovals and rectangular port heads.
http://www.maliburacing.com/ovalvsrect.htm

I thought about that too - the cost of new inconnel exhaust valves would approach the cost for the complete set of heads. He said they have around 250 hours on them, but I need to see them in person to make the call. They look tired in the pictures, but it's hard to tell anything from that. The article you posted definitely helps me to decide on the ovals. I can get the 781's for $100.

There is a guy on the chevelles.net forum (goes by VortechPro) who is apparently making some pretty stout numbers on 454 builds with the 236 casting peanut port heads. He is doing some port work on them, adding 2.19 / 1.88 valves, and going with a mild 226* 236* 112 LSA hyd roller. He is dynoing these things in excess of 550 HP. Apparently, it's all in the combo of parts.

The guy that is trying to sell me the 781 right down the street from me with a fresh valve job and very clean but with the small valves wants 900.

His bag's loose! You could score a nice set of lightly used Merlin ovals for that price easily. I guess I better buy up all the 781 castings that guy has for $100 / pair! ;)